Comparison of Digital and Film Stereo Photography of the Optic Nerve in the Evaluation of Patients with Glaucoma

Compressed 3D and 2D digital images versus standard 3D slide film for the evaluation of glaucomatous optic nerve features

SYNOPSIS

Clinicians can feel confident compressed three-dimensional digital (3DD) and two-dimensional digital (2DD) imaging evaluating important features of glaucomatous disc damage is comparable to the previous gold standard of stereoscopic slide film photography, supporting the use of digital imaging for teleglaucoma applications.

BACKGROUND/AIMS

To compare the sensitivity and specificity of 3DD and 2DD photography with stereo slide film in detecting glaucomatous optic nerve head features.

METHODS

This prospective, multireader validation study imaged and compressed glaucomatous, suspicious or normal optic nerves using a ratio of 16:1 into 3DD and 2DD (1024×1280 pixels) and compared both to stereo slide film. The primary outcome was vertical cup-to-disc ratio (VCDR) and secondary outcomes, including disc haemorrhage and notching, were also evaluated. Each format was graded randomly by four glaucoma specialists. A protocol was implemented for harmonising data including consensus-based interpretation as needed.

RESULTS

There were 192 eyes imaged with each format. The mean VCDR for slide, 3DD and 2DD was 0.59±0.20, 0.60±0.18 and 0.62±0.17, respectively. The agreement of VCDR for 3DD versus film was κ=0.781 and for 2DD versus film was κ=0.69. Sensitivity (95.2%), specificity (95.2%) and area under the curve (AUC; 0.953) of 3DD imaging to detect notching were better (p=0.03) than for 2DD (90.5%; 88.6%; AUC=0.895). Similarly, sensitivity (77.8%), specificity (98.9%) and AUC (0.883) of 3DD to detect disc haemorrhage were better (p=0.049) than for 2DD (44.4%; 99.5%; AUC=0.72). There was no difference between 3DD and 2DD imaging in detecting disc tilt (p=0.7), peripapillary atrophy (p=0.16), grey crescent (p=0.1) or pallor (p=0.43), although 3D detected sloping better (p=0.013).

CONCLUSIONS

Both 3DD and 2DD imaging demonstrates excellent reproducibility in comparison to stereo slide film with experts evaluating VCDR, notching and disc haemorrhage. 3DD in this study was slightly more accurate than 2DD for evaluating disc haemorrhage, notching and sloping.

Teleglaucoma: improving access and efficiency for glaucoma care

Teleglaucoma is the application of telemedicine for glaucoma. We review and present the current literature on teleglaucoma; present our experience with teleglaucoma programs in Alberta, Canada and Western Australia; and discuss the challenges and opportunities in this emerging field. Teleglaucoma is a novel area that was first explored a little over a decade ago and early studies highlighted the technical challenges of delivering glaucoma care remotely. Advanced technologies have since emerged that show great promise in providing access to underserviced populations. Additionally, these technologies can improve the efficiency of healthcare systems burdened with an increasing number of patients with glaucoma, and a limited supply of ophthalmologists. Additional benefits of teleglaucoma systems include e-learning and e-research. Further work is needed to fully validate and study the cost and comparative effectiveness of this approach relative to traditional models of healthcare.

The value of tests in the diagnosis and management of glaucoma

PURPOSE

To assess the noneconomic value of tests used in the diagnosis and management of glaucoma, and explore the contexts and factors that determine such value.

DESIGN

Perspective.

METHODS

Selected articles from primary and secondary sources were reviewed and interpreted in the context of the authors' clinical and research experience, influenced by our perspectives on the tasks of reducing the global problem of irreversible blindness caused by glaucoma. The value of any test used in glaucoma is addressed by 3 questions regarding: its contexts, its kind of value, and its implicit or explicit benefits.

RESULTS

Tonometry, slit-lamp gonioscopy, and optic disc evaluation remain the foundation of clinic-based case finding, whether in areas of more or less abundant resources. In resource-poor areas, there is urgency in identifying patients at risk for severe functional loss of vision; screening strategies have proven ineffective, and efforts are hindered by the inadequate allocation of support. In resource-abundant areas, the wider spectrum of glaucoma is addressed, with emphasis on early detection of structural changes of little functional consequence; these are increasingly the focus of new and expensive technologies whose clinical value has not been established in longitudinal and population-based studies. These contrasting realities in part reflect differences among the value ascribed, often implicitly, to the tests used in glaucoma.

CONCLUSIONS

The value of any test is determined by 3 aspects: its context of usage; its comparative worth and to whom its benefit accrues; and how we define historically what we are testing. These multiple factors should be considered in the elaboration of priorities for the development and application of tests in glaucoma.

Digital versus film stereo-photography for assessment of the optic nerve head in glaucoma and glaucoma suspect patients

PURPOSE

One of the leading methods for optic nerve head assessment in glaucoma remains stereoscopic photography. This study compared conventional film and digital stereoscopy in the quantitative and qualitative assessment of the optic nerve head in glaucoma and glaucoma suspect patients.

METHODS

Fifty patients with glaucoma or suspected glaucoma underwent stereoscopic photography of the optic nerve head with a 35-mm color slide film and a digital camera. Photographs/images were presented in random order to 3 glaucoma specialists for independent analysis using a standardized assessment form. Findings for the following parameters were compared among assessors and between techniques: cup/disc (C/D) ratio, state of the optic rim, presence of peripapillary atrophy and appearance of the retinal nerve fiber layer, blood vessels, and lamina cribrosa. The film-based and image-based diagnoses (glaucoma yes/no) were compared as well.

RESULTS

Despite high level of agreement across graders using the same method for the horizontal and vertical C/D ratio, (intraclass correlations 0.80 to 0.83), the agreement across graders was much lower for the other parameters using the same method. Similarly the agreement between the findings of the same grader using either method was high for horizontal and vertical C/D ratio, but low for the other parameters. The latter differences were reflected in the disagreement regarding the final diagnosis: The diagnoses differed by technique for each grader in 18% to 46% of eyes, resulting in 38.5% of eyes diagnosed with glaucoma by film photography that "lost" their diagnosis on the digital images, whereas 18.7% of eyes diagnosed as nonglaucomatous by film photography were considered to have glaucoma on the digital images.

CONCLUSIONS

Although there is consistency between 35-mm film stereoscopy and digital stereoscopy in determining the cup/disc (C/D) ratio, in all other parameters large differences exist, leading to differences in diagnosis. Differences in capturing images between digital and film photography may lead to loss of information and misdiagnosis. Further studies are needed to determine the reliability of the new digital techniques.

Utility of digital stereo images for optic disc evaluation

PURPOSE

To assess the suitability of digital stereo images for optic disc evaluations in glaucoma.

METHODS

Stereo color optic disc images in both digital and 35-mm slide film formats were acquired contemporaneously from 29 subjects with various cup-to-disc ratios (range, 0.26-0.76; median, 0.475). Using a grading scale designed to assess image quality, the ease of visualizing optic disc features important for glaucoma diagnosis, and the comparative diameters of the optic disc cup, experienced observers separately compared the primary digital stereo images to each subject's 35-mm slides, to scanned images of the same 35-mm slides, and to grayscale conversions of the digital images. Statistical analysis accounted for multiple gradings and comparisons and also assessed image formats under monoscopic viewing.

RESULTS

Overall, the quality of primary digital color images was judged superior to that of 35-mm slides (P < 0.001), including improved stereo (P < 0.001), but the primary digital color images were mostly equivalent to the scanned digitized images of the same slides. Color seemingly added little to grayscale optic disc images, except that peripapillary atrophy was best seen in color (P < 0.0001); both the nerve fiber layer (P < 0.0001) and the paths of blood vessels on the optic disc (P < 0.0001) were best seen in grayscale. The preference for digital over film images was maintained under monoscopic viewing conditions.

CONCLUSIONS

Digital stereo optic disc images are useful for evaluating the optic disc in glaucoma and allow the application of advanced image processing applications. Grayscale images, by providing luminance distinct from color, may be informative for assessing certain features.

Software-assisted optic nerve assessment for glaucoma tele-screening

Increased optic nerve head (ONH) cup-to-disc ratio (CDR) may indicate glaucoma but evaluation needs to be performed by a trained examiner. This research assessed new software to calculate CDR from ONH images. Digital stereoscopic ONH images from 28 subjects acquired during screening using a nonmydriatic 45-degree camera with 8.2-Megapixel resolution (Canon, Tokyo, Japan) were analyzed by 3 individuals with different levels of ophthalmic training: glaucoma specialist (GS), an optometrist (OD), and trainees. Images were logged and accessed by raters masked to each other's evaluations. Images from two groups were included: normal-appearing ONH (Group 1) and confirmed glaucoma (Group 2). All images were captured in DICOM format. Images were evaluated on a 32-bit, 1,600 x 1,200-pixel resolution monitor. EyeScape software (v. 7.4, Synemed, Inc., Benicia, CA) was used for CDR analysis. Software CDR determination requires an operator to place ONH disc and cup contour lines. Once lines were placed, the software provided CDR calculations (range 0.00-1.00). A total of 84 ONH evaluations were analyzed. Overall CDR mean, standard deviation, standard error of the mean, and mean difference from GS CDR evaluations were determined. Reproducibility was similar for all operators. The trainee had a small, statistically significant greater CDR in group 1 and 2 evaluations. Evaluation of ONH images for CDR can be performed using EyeScape software, by individuals with different levels of ophthalmic training. Accurate determination of CDR is important in tele-screening for vision-threatening diseases, and can aid in identifying subjects with suspicious ONH in need of specialty eye care.